This P01 Project is in response to NIH Guide Notice NOT-AI-02-023, calling for research to improve the prevention, detection, diagnosis, and treatment of diseases caused by potential bioterrorism agents. Francisella tularensis is a Class A biothreat that is poorly understood at virtually every level, largely due to its zoonotic origin and extreme biohazardous nature. Recently, the Working Group on Civilian Defense highlighted the need for tularemia research in a number of basic areas. This P01 project addresses many of these major research gaps by bringing together a talented group of investigators with diverse, but complementary, expertise and with shared interests in the molecular basis of bacterial pathogenesis. The principal theme of this Program is to study how F. tularensis models its outer cell surface and immediate external environment to carrv out its complex parasitic strategy. Project 1 (Dr. Simon Daefler) will explore the intracellular trafficking pathway of the F. tularensis-containing vacuole with emphasis on characterizing candidate virulence factors that ostensibly block fusion of the bacteria-containing endosomes with lysosomes. Project 2 (Dr. Eric Ransen) will investigate iron acquisition by F. tularensis and its influence on virulence expression. Project 3 (Dr. Kevin Mclver) will analyze products secreted by F. tularensis into the extracellular environment that may represent toxins and other virulence factors. Project 4 (Drs. Michael Norgard and Kayla Ragman) will identify and characterize the outer membrane proteins and lipoproteins of F. tularensis. Project 5 (Dr. Vanessa Sperandio) will explore the genetics of virulence expression by F. tularensis and develop new genetic systems for manipulating F. tularensis. A particular strength of this Program is its focus on Schu4, a strain of F. tularensis that is highly infectious for humans. Progress in the individual projects will be enhanced substantially by the sharing of new developments, reagents, and specialized facilities and technologies. The combined studies will further our basic and working knowledge of F. tularensis pathogenesis that likely will lead to new diagnostic, vaccine, and intervention modalities for tularemia.